Since the surface of an optical base material, specifically that of a plastic lens is easy to be scratched as it is, because a synthetic resin constituting the plastic lens (a plastic lens material) is low in its abrasion resistance, a hard coating layer is usually formed on the surface of a lens. Usually, when laminating a hard coating layer, its abrasion resistance can be improved; it has been known that the impact resistance of the plastic lens is decreased. Further, in order to inhibit reflected light from the plastic lens, an antireflection coating layer is laminated on the hard coating layer by depositing an inorganic oxide on the hard coating layer. It has been, however, known that when the antireflection coating layer is laminated on the hard coating layer previously laminated on the surface of the plastic lens, the impact resistance of the plastic lens is lowered more increasingly to be easily cracked. It has been, therefore, studied that a primer coating layer is inserted between a plastic lens and a hard coating layer for the purpose of improving the impact resistance. For a plastic lens of high refractive index, the refractive index of a primer coating layer laminated is important. This is because that an interference pattern is generated caused by the difference in refractive index between the plastic lens and the primer coating layer.
As a primer composition for a plastic lens of high refractive index that using a urethane resin has been usually known. Specifically, (i) a primer composition comprising a mixture of a urethane resin and inorganic oxide fine particles (Patent Literature 1), (ii) that comprising a mixture of a urethane resin, inorganic oxide fine particles and a hydrate of an organosilicon compound (Patent Literature 2), (iii) that comprising a mixture of a urethane resin, inorganic oxide fine particles and a urethane-forming monomer- and/or oligomer (Patent Literature 3), etc. have been known. Further, (iv)) a primer composition using a polyester resin and inorganic oxide fine particles has been also known (Patent Literature 4).
Such primer compositions as described above can give good adhesion to a specific plastic material and can improve the impact resistance of the specific plastic material. However, these primer compositions have problems that the adhesion is insufficient depending on the types of plastic materials constituting a plastic lens. In a case of a primer composition comprising a mixture of a urethane resin and inorganic oxide fine particles, there is a case where a primer coating layer formed is whitened, and there has been, therefore, still room for improvement.
Specifically, a primer composition disclosed in Patent Literature 1 has problems that it requires long time for curing of a primer coating layer and is inferior in workability, productivity, etc., in addition to such problems as described above. It has been considered that the causes of those problems are characteristics of a urethane resin itself used and an organic solvent added to a primer composition.
A primer composition disclosed in Patent Literature 2 has problems that the adhesion is insufficient depending on the types of plastic lens materials and a primer coating layer formed is whitened (due to the use of inorganic oxide fine particles as a mixture with a urethane resin). In addition to that, a primer composition disclosed in Patent Literature 2 has a problem in the storage stability sustainable to long term use due to the use of a hydrate of an organosilicon compound.
A primer composition described in Patent Literature 3 comprises an urethane-forming monomer as a third constituent component in addition to a urethane resin and inorganic fine particles. It is necessary to cure the urethane-forming monomer in order to form a primer coating layer. A curing treatment is carried out for a primer coating layer at high temperatures after coating the surface of a plastic lens with the primer composition. Therefore, when using such a primer composition for a plastic lens of low heat resistance, there are problems that a plastic lens is thermal-deformed or colored etc. Further, there has been a problem that the storage stability of a primer composition is not sufficient because of the use of a reactive urethane-forming monomer.
Patent Literature 4 describes a primer composition comprising a polyester resin and describes that inorganic oxide fine particles can be added to the primer composition. As a result of the study of the inventors of this invention, however, it has become clear that a primer composition comprising a polyester resin and inorganic oxide fine particles has a problem that the adhesion is insufficient depending on the types of plastic lens materials.
In recent years, an aqueous dispersion of urethane resin has been used for a primer composition for improving the impact resistance of plastic lens from the view point of environmental problems. However, when an aqueous dispersion of urethane resin is used, there are many problems in low wettability to a plastic lens and appearance of the coating such as smoothness, etc. In order to solve such problems, an organic solvent is added for improvement of the wettability and the smoothness of the coating. However, a new problem occurs sometimes in that the storage stability of the primer composition itself lowers.
For an optical article such as a plastic lens, etc., a photochromic coating layer comprising a photochromic compound is formed on the surface of a plastic lens in order to give a photochromic properties to a plastic lens. The photochromic properties herein used are defined as a reversible action in which when an object is irradiated with light comprising ultraviolet rays such as sunlight, light of a mercury vapor lamp, etc., it becomes discolored rapidly, and when irradiation of light is terminated and it is placed in a dark place, it returns to its original color. Such a photochromic coating layer is formed by applying a photochromic coating agent comprising a photochromic compound and a polymerizable monomer on the surface of a plastic lens and then curing it (hereinafter such a method of forming a photochromic coating layer is referred to as just “coating method” as the case may be).
In the coating method of a prior art, a photochromic coating layer is formed directly on the plastic lens. In recent years, however, in order to improve more highly the adhesion of the photochromic coating layer and the plastic lens, a method has been adopted for forming a photochromic coating layer after forming a primer coating layer on a plastic lens. Specifically, in order to form the primer coating layer for the photochromic coating layer, a method has been known of using a primer composition comprising a moisture-curable polyurethane resin (Patent Literature 5) or a primer composition comprising urethane resin emulsion (Patent Literature 6). These methods can enhance the adhesion of the photochromic coating layer and the plastic lens. There is, however, still room for improvement in the respects described below:
That is to say, in the method described in Patent Literature 5, a primer composition comprising a moisture-curable polyurethane resin and/or its precursor, and a solvent having a boiling point of 70° C. and above and a solubility parameter of eight (8) and above is used. However, when a primer coating layer is formed on the surface of a plastic lens of a polycarbonate, it occurs that a solvent constituting the primer composition dissolves excessively the surface of the plastic lens. In order to prevent that, a different film or layer for prevention must be newly formed on the surface of the plastic lens. Therefore, there is still room for improvement in operability. Such a primer composition comprises inorganic oxide fine particles. There is, however, a problem that a refractive index is low, because of difficulty of mixing of inorganic oxide fine particles.
In the method described in Patent Literature 6, a primer composition comprising an emulsion in which a urethane resin is colloidal dispersed in a dispersion medium. By the use of such a primer composition, the adhesion of plastic lens and a photochromic coating layer can be sufficiently secured. There is, however, a problem that when inorganic oxide fine particles are mixed, the primer coating layer is whitened.
As described above, in the primer composition used in the production of a photochromic plastic lens according to the coating method, the development of a primer composition applicable to a plastic lens of various types of materials has been expected. Further, the development of a primer composition has been expected which is capable of improving not only the impact resistance of a plastic lens, but also the adhesion of a plastic lens and a photochromic coating layer.